This invention relates to certain melt-fusible copolyimides useful in the manufacture of sheets, films, fabricated articles, and composite structures.
For the purpose of the present disclosure and claims, the term "melt-fusible" means that the material can be heated without significant decomposition above its glass transition temperature (Tg), if it is amorphous, or above its crystalline melting point (Tm), if it has crystallinity, and coalesced under pressure. Some of the polyimides of the present invention also are melt-processible, which means that they can be fabricated by conventional melt processing techniques, such as extrusion and injection molding, in which the melt passes through an orifice.
Polyimides are well known to the art and have been described in numerous patents and in scientific literature. A class of melt-fusible polyimides has been reported in the copending application Ser. No. 534,208 of T. P. Gannett and H. H. Gibbs, filed Sept. 21, 1983, now U.S. Pat. No. 4,576,857. In all the polyimides of that application, the acid portion is derived from pyromellitic anhydride. Normally, it is very difficult to make melt-fusible polyimides based on pyromellitic anhydride and an ordinary aromatic diamine; therefore the Gannett et al. application proposes the use of certain specific aromatic diamines containing one or two ether or thioether groups.
Those special diamines, however, are not all readily available, and those that are available tend to be expensive. It thus is desirable to replace at least a portion of such a special diamine with a cheaper, more readibly available aromatic diamine.